Technical Field of the Invention
This invention relates generally to electrical equipment and more particularly to electric motors.
Description of Related Art
As is known, there are various types of electric motors and an almost endless variety of uses for them. For instances, an electric motor may be an AC motor (e.g., synchronous or induction), a servo motor, a DC motor, or an electrostatic motor (e.g., magnetic motor) and may be used in applications that range from micro-electrical systems (MEMS), to food processing equipment, to household appliances, to power tools, to automobiles, to toys, to large manufacturing equipment, etc. Basically any electrically powered device that uses mechanical motion includes an electric motor.
Due to the vast uses of electric motors, they come in an almost endless variety of sizes, shapes, and power levels. For instance, the size of a MEMS motor is small enough to fit on an integrated circuit and supplies nano-watts of power, while a large manufacturing equipment motor may be tens of feet in diameter supplying hundreds of thousands of kilowatts of power. Note that power of electric motors is sometimes expressed in horsepower, where one horsepower equals 746 watts.
Regardless of the size, shape, and power level, many types of electric motors include a stator and a rotor. The stator includes coils that produce an electromagnetic field. The rotor includes a die cast squirrel cage assembly and/or magnets that, when in the presence of the electromagnetic field, causes the rotor to rotate. Often, the speed at which the shaft of the rotor rotates is not the desired speed of the device incorporating the motor. In these instances, the motor is coupled to a separate gearbox.
As is known, a gearbox provides a speed-torque conversion. For example, a gearbox may be used to slow the rotation down and increase the torque. As another example, a gearbox may be used to increase the speed of rotation and reduce the torque. In addition, a gearbox may be used to change the axis of rotation such as in a right angle gearbox.
When a motor and/or a gearbox are used in an agriculture application (e.g., irrigation equipment), it must be able to withstand constant exposure to water, agriculture chemicals, and/or other environmental conditions. For these applications, the motor is often encapsulated with a thermally conductive polymer. The geometry of the motor (in particular, the stator), however, impairs the penetration of the encapsulating material around the copper wire of the stator windings, which leaves small sections of the stator winding insulation unprotected by the encapsulating material that corrode over time and cause the motor to fail.
In an addition, motors that are powered by a single or three-phase power source use an insulating film between stator coils of different phases. The end-turns of a coil are formed in spike and block presses and then connected with metal crimp connector to lead wires, which are insulated with coated fiberglass tubing. Over time, such motors are subject to failure if varnish or insulating film fails due to a manufacturing variation (e.g., not perfectly positioned to insulate every portion of the coils) and/or if movement of the end turn wires causes internal shorting of the windings.